I took up a job needing a 25 mile bike ride plus Intercity 125 train journey at peak commuter hours into London. I came from a trade background where I handled many folding bike sales. So I knew what I was looking for from having tested and demonstrated almost all of them with the exception of the real budget efforts.
I settled on the most basic of aluminium framed Dahon models even though I could have bought a posh one. There was a trade-off between flexibility and features. The dynamo hub, hub gear and other features were not what I needed, they also came with a weight penalty and complicated the fold.
Why it had to be Dahon for me was the patents. The hinges and other folder specific parts are patented and Dahon have the best portfolio of patents. They make plenty of bikes for other people, e.g. Ridgeback, however, those tend to be last year's models, e.g. without the handlebar post that is reliable.
The supposed Rolls Royce 'Brompton' bikes are not a patch on the basic Dahon models. The two plastic wheels either side of the seat post catch on people's calves leaving marks grubbier than what you can get with a chain. Then there is the way that rear 'suspension' works, the bike is basically un-hinged. The catches are all made of heavy steel and require a lot of fiddling, on the Dahon bikes the designs for these parts are a lot smarter, easier on the eye and lighter. The clip on the left-hand side of the front wheel is also prone to breaking. As for be wheel size, smaller is not better, particularly if you want tyre choice. As for those ridiculous pedals I think Heath Robinson designed them. Ergonomics on a Brompton have a lot to be desired and why don't they come with a useful selection of gears? For the life of me I do not know why they are considered preferable by those that ride them, it is almost like the Cult of Apple.
Brompton bikes are expensive in part because they are made in Great Britain where wages are higher than in China, Macau, Taiwan or wherever else Dahon make their bikes. But are they really higher? I have seen adverts for jobs at the Brompton factor and they are barely over minimum wage. You cannot work there and have mortgage, family and a holiday every year. Meanwhile, the workers in the Dahon factory do not have ridiculous housing costs that Londoner's have to pay for, they get paid a competetive wage for their area, not minimum wage + a pittance.
The big-headed attitude that is the Brompton brand is a turn off for me, plus the religious zeal of the fanbois. The product is not as good as they claim it to be, the scarcity value due to them not having a big enough factory makes people think they are more desirable than they are.
Meanwhile, the Dahon models are more like bikes that are designed first and foremost as bikes but have the added benefit of folding. The patents are top notch. The ergonomics work for anyone over 5'2" and under 6'3". As for the seatpost, it is alloy, works without fail on maximum extension and has a pump inside. Oh, and a clamp that you don't have to faff with.
As for the other brands at the cheaper end of the market, they don't have the special Dahon patents either. They are me-too products that are not researched or developed properly. You might as well get a thirty year old small-wheel shopping bike instead of any of today's budget folders - at least the chrome will be better quality.
One way of looking at it is to take a car analogy. The Dahon is like the quality Honda models (see that anagram), the budget models are like a Chinese clone of a 10 year old Kia Pride and the Bromptons are like a practically impractical Caterham 7 (without the speed and handling). The Honda might not have the cult following of the Caterham but it gets you from A to B and you have a choice of models to choose from.